Broach



Feb 17, 1948. NY 2,436,325

BRO CH Flled Nov. 27, 1943 Patented Feb. 17, 1948 2,436,325

BROACH John K. Penny, Grosse Pointe, Mich, assignor to Spirex Broach Corporation, Detroit, Mich., a corporation of Michigan Application November 27, 1943, Serial No. 511,946

10 Claims. (01. 29-951) This invention relates to breaches such as are extensively used in mass production for finishing large quantities of similar workpieces.

The use of broaches for finishing workpieces 2 in the tapered part of the spirally fluted section in their finished condition:

Fig. is a view similar to'Fig. 4 buttaken on the line 5-5 of Fig. 2 showing the broach teeth and particularly workpieces provided with a hole 5 at the finishing end of the spirally fluted broach of circular or other cross-sectionalcontou has section, and increased proportionately with the spread of mass ig. 6 is a somewhat diagrammatic view show- ,production methods. Although broaches have ing the manner in which the broach teeth are been very widely used for many years, difficulty is v n their final sh pe- 1 frequently experienced in their use because of 10 Fig.7 is a view similar to Figs.'4 and 5 showing the tendency of a broach provided with cutting a modified construction in which the broach is teeth in the finishing section thereof which exp v With burnishing t eth at t e en of t tend at right angles to the longitudinal, axis of shing section. e the broach to leave tooth or chatter marks in the S S n in 1 f the d aw the broach \w0rkp ece An even more serious bjectio in HI consists of a number of sectionsas indicated this type of broach is the production of longiby the reference characters II, I 2, [3, I4, I 5 and tudinally extending scratch lines resulting from Section 0f the breech is provided With nicks inthe cutting edges of the teeth which in teeth which.v as a y s extend at a ri ht continued use tend to be reproduced in the followangle to theeXiS 0 h b While e t s H ng teeth, An th ime t or bje tionable y '20 to IE, which are semi-finishing and finishing" ture of broaches generally is their tendency to cut t e s, are provided With sp y arran ed flutes the hole to be finished slightly larger in diameter or teeth, the flutes o c on b v of difat the end of th hole wher th b h is ferent hand than the flutes of the adjacent sectered, thus resulting in what is known as a belltion, all a Clearly Shown h- AS e Spi al mouth hole. In order to avoid the objectionable was utting teeth tend to pr d e nu p ral tooth or chatter marks of what may be termed a Chip S av n W eh cu s th h the flute straight tooth broach many broaches have been and out the back end thereof; ,1 have located at made with spiral teeth in the finishing section. he end of c a y fluted sec a p The use of th i al b c as heretofore com breaking or holeclearing tooth 20. Each of these structed, however, is subject to the objection that .30 clearing teeth is of Slightly Smaller diameter t n the broach either tends to screw into the work or that of e finish s of spir l section whichit. tends to exert a great pressure on the work which follows- Each of the Sections II 110 I5 a e of tends not only to rotate or turn the work but also Similar Construction; there being a c ease in to distort o expand t workpiece and thus diameter of a few thousandths of an inch from duce an inaccurate sized h l one section to another. As the construction of The present inv nti n h for t principal each spiral section of the broach is similar, a 'de- .jiect to provide a new and improved construction scription of one Section Will Suffice for l- The for a broach whereby t objection bl f t broach section l3 which is shown in the enlarged above noted will be obviated, and a construction View 2, is typical of each of e Other such that i dditi t eliminating tooth and 40 tions andit consists of a plurality of spirally fluted chatte ark an extremely high fini h 1 be teeth which in the particular constructional eximparted t th urfac of t hole and also the ample illustrated are composed of two separate work will be held precisely to the required finished splrals as they are usually designated in the dimension 7 art, starts 2|, 22.

Th above and other objects f the present In constructing the broach of the present invention will appear more fully from the following Ventlon sitter the Stock has been rough turned more detailed description and by reference to the to the desired the flutes or teeth are formed accompanying drawings forming a part hereof by followmg h same procedure as that wh r Ployed gh n a buttress-shaped thread hav- Fi 1 is a side elevation of a broach constructed g; tlie l re233 13;? rit i fn te i' geih gfifi yggg g gilvigtzriaggance with the principles of the present indicated at 23 and being tangent to the straight 3 flank 24 which forms the front cutting face of Fi 2 1s a greatly enlarg d v Of that the broach teeth. The other flank 25 of the thread tion of the broach shown n Fig- 1 enclosed Within extends at an angle such as to establish a desired thedo n -da l s e e land width as indicated at 26 in Fig. 4 of the Fig. 3 is a transverse section on the line 33 of drawings.

After the flutes or teeth'are rough formed in Fig. 4 15 a still further enlarged section taken any suitable way as by a thread chasing operon the line 44 of Fig. 2 and showing the teeth ation in a, lathe as just described and the toolis hardened, the outside diameter of the teeth are first groundstraight for the entirelength of any particular. spirally fluted section, such grinding operation being similar to that employed for grinding a cylindrical plug gauge.

After the teeth have been ground cylindrically for their.

entire length, the lathe center may then be offset as indicated in Fig. 6 of .thesdrawings .to the proper amount for securing the desireditaper-of the cutting'face of the broach teeth, the tops of the teeth arethen backed off sharp to a. cutting .edge by a wheel dressed to the, proper angle,

this work also being accomplished by having the tailstock of the lathe offset at thessame taper,

as was used for-forming the tapered part of 'the.. broa'ch section. As a result of thisprocedure thebroach teeth in the entire tapered portion of -each section will be backed off-to a sharp cut- .tingedge and, because of the fact that the straight section of the .broach at thefinishing end is set off-center, as the grinding .wheel runs through onto the straight section of the broach .a straightland of .gradually increasing width will beleftupon the teethof the straight-section, the amount of increase in the width of the'jland obviously depending entirely upon the angle of taper in the, tapered portion of the .broach.

'In'the enlarged view of Fig. 2 the parallellines indicated by the referencecharacter 30, shown .at each side of the breach, are parallel with the longitudinal axis of the'broach and serve to indicate the diameter of the straight cylindrical teeth, threeof which, as indicatedby the referencecharacters am, 351) and 3lc, are left at the finishing end of the broach section. The remainder of the broach teeth which are indicated by the reference character 1'32 are tapered, as clearly indicated in Fig. 2 of the drawing.

.In Fig. 4 of the drawing is shown a number of theteeth 32 in greatly enlarged cross-section, the dotted line portion indicated by the reference character 33 indicating that portion of the top of the broach teeth that has been ground away so as to produce a tooth having a sharp back-off 34 that terminates in the sharp cutting edge .35.

In Fig.5 of the drawing the teeth 3la, 3lb and Sic are shown in greatly enlarged cross-section .and the reference characters a, b and 0 indicate the varying width of land that is formed on each of the'finishing teeth as thegrinding wheel used for backing off the teeth runs out over the straight cylindrical portion of the broach due tothe ofisetting of the tailstock of the lathe in performing this backing-off operation. As will be clearly apparent from thedrawing, the land a is of, less width than the land I) and the latter is less in width than the land 0. The distinctive feature of the land on the straight cylindrical portion of the teeth is that it starts from zero width and gradually reaches a maximum at'the extreme end. As a result each time the broach is sharpened the straight cylindrical finish sized section always consists of a portion in of the workpiece or distortion thereof.

else and accurate limits.

which the finish diameter teeth begins with sharp edged tooth and wi-th =a land-of gradually increasing width immediately followihgthe sharp edge tooth insuring the cutting of the hole accu- 1. rately to the required dimension and the following land tending to produce an exceptionally smooth and high burnished finish. And further wa.muchlonger= period of service of the broach is secured than-ifthe broach teeth were backed ofi sharp'for-the full length thereof.

I have found that for best results the helix angle of the'spirally' fluted portions of the broach should preferably be between 5 to 35", an angle I in the order of 12 to 15 being preferred. When the helix angle of the spirals are kept within the limits above set forth, there is no tendency for the broach to revolve as it is beingpushed or pulled through the workpiece. Neither is there any tendency for the broach to cause rotation A constant and uniform pressure is applied to the workpiece and because of the helix angle of the teeth, the production of tooth or chatter marks in the hole is obviated. Furthermore, there is no tendency to produce bellmouth at the end of the hole where'the broach is entered and an extremely high finish is obtained on the broached surface. Likewise, the finished diameter of the hole broached can be kept within the more pre- The use of the spiral teeth extending at a helix angle as described results in the teeth performing a skewed slicing cutias distinguished from a straight chop-like cut.

The use of spiralsof opposite hand in each adjacent spirally fluted sectionalso serves to contribute materially towards the elimination of "tooth and chatterimarks and to assure the prothereof one or more burnishingteeth Ell. These teeth as shown have the sides of the tops thereof of curved configuration as indicated at 400,, which merge with the flats or lands 49b. In other words, the teeth are rounded and are not provided with a sharp cutting edge. The rounding of the teeth will obviously cause them to perform a burnishing function or action such as would be'performed by the use of the hand burnishing tool. This results in compressing the particles of the surface skin of the workpiece and produces a high glossy and polished finish on such surface. These-burnishing teeth perform a continuation of the spirally fluted teeth and are cut originally in the same manner and at the same time as the spiral cutting teeth, but in the finishing of the broach these burnishing teeth instead of being ground to a sharp cutting edge are ground by a formed grinding wheel or in any other suitable way to form the rounded surfaces shown in the drawing on the tops of the teeth.

While I have shown the broach illustrated in the drawing as being provided with two separate spirals or starts it will, of course,be understood that the number of starts may be varied as desired. Ordinarily the number of starts employed will be increased with an increase in the diameter of the broach. For small diameter breaches, two starts will ordinarily be employed, whereas for larger broaches, say three or four inches in diameter, the number of starts may for example be increased to as many as eighteen starts.

Although I have shown in Fig. 1 a broach having five spirally fluted toothed sections and one straight toothed roughing section, it will, of course, be understood that any desired number of spiral sections may be employed either with or without a straight toothed roughing section and that the broach obviously may be constructed of any desired diameter, length or cross-sectional configuration depending upon the nature of the work to be produced.

While I have shown a constructional example of a broach that has proven highly successful in actual commercial usage, it will, of course, be understood that many changes, variations and modifications of the particular constructional example selected for the purpose of illustration may be resorted to Without departing from the spirit of the invention as set forth in the claims hereunto appended.

I claim:

1. A broach having a rough cutting section having teeth extending at right angles to the longitudinal axis of said broach and a plurality of finishing sections each having spirally fluted teeth extending at an angle to said axis, the teeth of one spirally fluted section being of opposite hand to the spirally fluted teeth of an adjacent section, and a chip-breaking and hole clearing tooth between each adjacent broach section.

2. A broach having a rough cutting section having teeth extending at right angles to the longitudinal axis of said broach and a plurality of finishing sections each having spirally fluted teeth extending at an angle to said axis, the teeth of each adjacent spirally fluted section being of opposite hand to the spirally fluted teeth of the adjacent section, and the teeth of said spirally fluted section extending at a helix angle of from 5 to 35 to planes at right angles to the longitudinal axis of said broach.

3. A broach having a rough cutting section having teeth extending at right angles to the longitudinal axis of said broach and a plurality of finishing sections each having spirally fluted teeth extending at an angle to said axis, in which the spirally fluted section of said broach is tapered for the major portion thereof and the teeth in the remaining portion are of straight cylindrical shape.

4. A broach having a rough cutting section having teeth extending at right angles to the longitudinal axis of said broach and a plurality of finishing sections each having spirally fluted teeth extending at an angle to said axis, in which the teeth of the major portion of said spirally fluted sections are tapered and are backed off to a. sharp cutting edge.

5. A broach having a rough cutting section having teeth extending at right angles to the longitudinal axis of said broach and a plurality of flnishing sections each having a spirally fluted tooth section extending at an angle to said axis, the teeth of the major portion of said section being tapered and backed ofi to a sharp cutting edge, and the remaining portion of the teeth in said section being of straight cylindrical contour and provided with a straight land which increases gradually in width from zero to a maximum at the extreme finishing end of said straight cylindrical portion.

6. A broach having a rough cutting section having teeth extending at right angles to the longitudinal axis of said broach and a plurality of finishing sections each having spirally fluted teeth extending at an angle to said axis, the teeth of one spirally fluted section being of opposite hand to the spirally fluted teeth of the adjacent section, in which the spirally fluted section of said broach is tapered for the major portion thereof and the teeth in the remaining portion are of straight cylindrical shape.

7. A broach having a rough cutting section having teeth extending at right angles to the longitudinal axis of said broach and a plurality of finishing sections each having spirally fluted teeth extending at an angle to said axis, the teeth of one spirally fluted section being of opposite hand to the spirally fluted teeth of the adjacent section, in which the teeth of the major portion of said spirally fluted section are tapered and are backed off to a sharp cutting edge.

8. A broach having a rough cutting section having teeth extending at right angles to the longitudinal axis of said broach and a plurality of finishing sections each having spirally fluted teeth extending at an angle to said axis, in which the teeth of the major portion of said spirally fluted section are tapered and are backed off to a sharp cutting edge and the remaining portion of the teeth in the spirally fluted section are of straight cylindrical contour and are provided with straight lands of gradually decreasing width.

9. A broach having .a spirally fluted tooth section extending at an angle to said axis, the teeth of the major portion of said section being tapered and backed 01f to a sharp cutting edge, and the remaining portion of the teeth in said section being of straight cylindrical contour and provided with a straight land which increases gradually in width from zero to a maximum at the extreme finishing end of said straight cylindrical portion.

10. A broach having a spirally fluted cutting tooth section extending at an angle to said axis, the teeth of the major portion of said section being tapered and backed oil to a sharp cutting edge, and the remaining portion of the teeth in said section being of straight cylindrical contour and provided with a straight land which increases gradually in width from zero to a maximum at the extreme finishing end of said straight cylindrical portion, and a hole-clearing tooth slightly smaller in diameter than the finishing end of said spirally fluted cutting tooth section and rearwardly spaced from said end.

JOHN K. PENNY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,724,669 La Pointe Aug. 13, 1929 1,724,511 Perkins Aug. 13, 1929 2,255,140 Waring Sept. 9, 1941 2,292,900 Schmidt Aug. 11, 1942 1,935,774 Halborg Nov. 21, 1933 FOREIGN PATENTS Number Country Date 343,496 Great Britain Aug. 13, 1929 4,068 Great Britain Feb. 19, 1912 547,347 France Dec. '7, 1922 

